QuestionQUESTION: hi i have an alpine cda7873 aftermarket radio and i am installing it into a 1995 merc gran marquis i have all of the wires hooked up correctly but when i plug it in no sound but if the plug is half way out there is sound out of certain speakers do you have any idea what the problem is
ANSWER: Hi Dennis,
I'd probably start by inspecting the plug for bent or damaged pins. If two of the pins in the harness are contacting each other when the plug is inserted, it could result in a short circuit that would cause the head unit's internal amplifier to shut down.
Another possibility is that you have a defective speaker or shorted speaker wire somewhere else; possibly in the harness connections, or at a speaker location (especially if you've installed new speakers). The result would be the same: when the shorted wire is connected to the head unit's output, it causes an internal amp shut-down. Once the wire is no longer connected, the amplifier can work properly again. You might be removing the bad connection when you unplug and replug the connector; when the amplifier starts working again, you can hear the sound through the remaining speakers.
Hope this helps!
Brian
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QUESTION: it doesnt happen when the factory radio is plugged in. all of the speakers work
ANSWER: Hi,
I'm assuming you're using an adapter harness with the new head unit. If there are bent pins, I'd expect them to be in the adapter harness, not the factory plug.
The fact that the stock radio works without a problem makes me think that the trouble must be either in the adapter harness, or in the wiring between the harness and the new head unit.
There are a couple options for the factory audio system in this car. Looking at the factory radio plugs, are they two long 8-pin plugs, about the same size; or is there one long 8-pin plug and a second plug with smaller pins and more of a square shape?
Brian
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QUESTION: it is two long 8 pin plugs and the harness is brand new and all of the wires are hooked up correctly with none of them touching
AnswerOkay, that makes the "bent pin" theory less likely. It means that your car doesn't use a factory amplifier. The factory amp is common in the Grand Marquis, and the plug used in the amplified systems has smaller pins that bend easily. In the base model systems, that doesn't usually happen.
Assuming you don't have a defective head unit, then the most likely cause is a bad speaker or shorted speaker wire. There are two ways you can test for this:
First, if you have a digital multimeter with a continuity function, you can test each of the speaker wires for continuity with chassis ground. Set the meter for continuity, connect the black probe to a ground point (ie, the outer ring of the cigarette lighter) and probe each of the speaker wires with the red probe. If you find continuity with ground on any of the wires, then either the speaker is defective, or the speaker wire is shorted against chassis metal somewhere between the speaker and the head unit plug. (All the speaker wires are in the black factory plug).
If you don't have a meter, you can try disconnecting all the speakers except one. If the head unit plays through one speaker, connect each of other speakers, one at a time, until you find the speaker connection that's causing the sound to shut down.
The fact that the stock radio works might not rule out a shorted speaker wire or a speaker problem. Many factory radios (especially older ones) don't have the built-in protection circuits that are standard in after-market head units. That means a shorted wire won't necessarily make the factory deck's amplifier shut down, but will still kill the sound in an after-market deck.
Good luck!
